1. Field of the Invention
The present invention relates to a communication apparatus that specifies network, a control method therefor and a storage medium.
2. Description of the Related Art
There becomes widespread a VoIP (Voice over Internet Protocol) technique of communicating voice on an IP network, which is a technique of converting an analog voice signal to digital data by PCM (Pulse Code Modulation) in real time (PCM data conversion) and converting the digital data (PCM data) to a voice IP packet to perform voice communication on an IP network.
As a call connection protocol on the IP network, a SIP (Session Initiation Protocol) is used. Further, there becomes widespread a VoIP gateway (hereinafter referred to as “the VoIP GW”) for communicating voice between an IP telephone network and an analog telephone network.
There is used a technique, referred to as “the pseudo voice communication”, of converting an analog signal of a G3 FAX apparatus in conformity with ITU-T Recommendation T.30 to a voice IP packet to communicate with a G3 FAX apparatus connected to an analog telephone network via a VoIP GW, with the IP packet as voice.
Further, there also starts becoming widespread an IP FAX apparatus in conformity with ITU-T Recommendation T.38, which converts a signal of a G3 FAX apparatus compatible with T.30 to an IP message on an IP network and transmits the IP message in real time.
Furthermore, some VoIP GWs have a mutual conversion function of performing protocol conversion between T.38 and T.30 in real time.
Via the VoIP GWs having the mutual conversion function, it is possible to perform communication between the IP FAX apparatus compatible with T.38 and the G3 FAX apparatus compatible with T.30.
FAX communication by T.38 has an advantage of, in comparison with the pseudo voice communication requiring a voice band, enabling the band width to be decreased, enabling higher-speed communication to be performed because there is no restriction by the modulation speed of a modem.
On the other hand, the pseudo voice communication has an advantage of realizing even communication with a G3 FAX apparatus connected to a conventional analog telephone network connected to an IP network at a gateway, as described above.
Many of the conventional G3 FAX apparatus each are adapted such that a telephone can be connected thereto, whereby connecting the telephone to the G3 FAX apparatus realizes manually dialing or makes the telephone conversation, etc.
On the other hand, there has been devised a communication apparatus which can be connected to a telephone by using an SLIC (Subscriber Line Interface Circuit) in order to realize a telephone conversation via an IP network (see Japanese Laid-Open Patent Publication (Kokai) No. 2003-18292, for example).
The SLIC performs an analog-digital conversion process by a voice codec such as G.711. Therefore, use of the SLIC makes it possible to perform a telephone conversation using an IP network by converting a voice signal input from a telephone to PCM data and transmitting the PCM data to the IP network or by returning a voice packet received from the IP network to analog voice before outputting the analog voice to the telephone.
Furthermore, since the SLIC is capable of generating a telephone call signal or various kinds of tone signals and detecting DTMF (Dual Tone Multi-Frequency) generated by a telephone, it is possible to perform telephone line emulation.
Thus, since use of the SLIC in the IP FAX apparatus makes it possible to connect a telephone to an IP network without via a telephone line, even use of the IP FAX apparatus realizes manually dialing or makes a telephone conversation as in the case of use of a conventional G3 FAX apparatus.
Further, some of recent IP FAX apparatuses each is capable of connecting to a plurality of kinds of networks to perform simultaneous communication, which realizes not only communication with an internal IP network (hereinafter referred to as the “intranet”), but also communication with an analog telephone network via a VoIP GW and communication with an NGN (Next Generation Network).
When performing IP FAX communication using such an IP FAX apparatus, it is necessary to appropriately specify a transmission destination of an INVITE signal as a connection request signal of the SIP, according to a network including the communication destination.
Specifically, when the network including the communication destination is an intranet, call connection control is performed by a SIP server connected to the intranet; accordingly it is necessary to specify the address of the SIP server as the transmission destination of the INVITE signal.
When the network including the communication destination is an NGN, the IP FAX apparatus and the NGN are connected via a Home GW (hereinafter referred to as the HGW) or an Office GW (hereinafter referred to as the OGW); accordingly, it is necessary to specify the address of the HGW or the OGW to which the IP FAX apparatus itself is connected as the transmission destination of the INVITE signal.
Further, if the communication destination is connected, as a terminal, to an analog telephone network connected to a VoIP GW, it is necessary to specify the address of the VoIP GW as the transmission destination of the INVITE signal.
As described above, in a case where the IP FAX apparatus is simultaneously connected to a plurality of IP networks, it is necessary to not only input a telephone number but also specify an IP network including the communication destination, when making a call.
Therefore, the ordinary IP FAX communication starts communication after specifying the IP network including the communication destination, from the user interface of an IP FAX apparatus simultaneously when a user inputs a telephone number.
When using an IP FAX apparatus compatible with a telephone function, the user manually dials on a telephone connected to the IP FAX apparatus. Thus, if the telephone is placed away from the IP FAX apparatus, it is difficult to specify the IP network including the communication destination, from the user interface of the IP FAX apparatus.
Methods for switching from an extension to an outside line on a telephone connected to an analog telephone network, include a method using a dial prefix and a method using hooking.
When the telephone is connected to the analog telephone network, there occurs a predetermined dial tone. Here, a dial tone for the extension and a dial tone for the outside line are different from each other, which causes the user to determine which of the extension and the outside line the telephone is connected to.
On the other hand, when the telephone is connected to the IP FAX apparatus, there occurs no dial tone, which disables the user to determine which IP network the IP FAX apparatus is connected to, and whether or not the telephone can be connected to a plurality of IP networks.
Therefore, the user cannot determine whether or not it is necessary to perform an IP network specifying process before dialing.